<?php
function breedable_meta_boxes()
{
	global $post;
	$pagename = 'breedable';
// api code box
add_meta_box( 'breedable_additional_desc', __('Additional Description', 'breedable'), 'breedable_additional_desc', $pagename, 'normal', 'high' );
}
add_action( 'admin_footer', 'breedable_meta_boxes' );

function breedable_additional_desc() {
?>
    <textarea name='additional_description' id='additional_description' cols='40' rows='5' ><?php echo esc_textarea( get_post_field( 'post_excerpt', get_the_ID() ) ); ?></textarea>
<?php

}
?>